Optical discs store information that can later be optically read. The optical disc may be a digital video disc (DVD), a compact disc (CD), a Blu-Ray disc (BD), or other types of data storage media that use optics. In some types of optical discs, the data is stored on spiral tracks as either pits or lands. Pits represent one data value and lands represent a different data value.
An optical disc is read by shining a laser onto a track and sensing reflected light using a photoelectric sensor. The pits cause reflected light to add destructively at the photoelectric sensor, while the lands cause reflected light to add constructively at the photoelectric sensor. The photoelectric sensor generates an electrical signal that corresponds to how much light is received. A read channel decodes the electrical signal to recover the data stored on the optical disc. However, a defect such as a speck of dust, dirt, or a scratch on the optical disc can make data stored at the defect location difficult or impossible to read. A better way of reading optical discs at defects may be desired.